The present invention relates to an image forming apparatus of the type having a developing unit for developing a latent image electrostatically formed on a photoconductive element or similar image carrier by using a developer, or toner, and using a toner cartridge which is filled with a toner and loaded in the developing unit. The present invention also relates to an improvement in the toner cartridge applicable to such an apparatus.
In an image forming apparatus of the type described which may be implemented as an electrophotographic copier, printer or facsimile machine, for example, a toner stored in a developing unit is consumed every time an image is formed and, in due course, the toner supply becomes short. A toner cartridge filled with a toner has customarily been loaded in the developing unit in order to supply the toner as needed. To promote accurate manipulations for such a toner supply, the image forming apparatus is usually constructed to sense the short supply of toner in the developing unit and display the shortage on a display, thereby urging one to supply a more toner. Specifically, one is urged to remove the used toner cartridge and then load a fresh toner cartridge in the developing unit.
The prior art apparatus, however, provides no visible instructions as to what the operator is expected to execute after dismounting the used toner cartridge or after mounting a fresh toner cartridge. This often perplexes the operator concerning the kind of work which should be done after the removal or insertion of a toner cartridge. Moreover, it may occur that after mounting a fresh toner by a troublesome manipulation one forgets an expected manipulation for feeding the toner to the developing unit, i.e., the image forming operation continues without the toner being supplied at all.